The invention relates to internal combustion engines. The invention relates more particularly to the control of exhaust gases in such engines. In normal operation of a reciprocating internal combustion engine the exhaust gases are removed, after each compression stroke, by the sweep of a piston, during an exhaust stroke, through a cylinder to force burnt gases into an exhaust manifold and towards an exhsaust pipe.
U.S. Pat. No. 1,586,778 discloses a four stroke reciprocating piston internal combustion engine (7) having several cyliners with inlet and exhaust valves adjacent tops of the respective cylinders and an exhaust chamber (6) for collecting exhaust gases produced by the engine in use, said engine including a vacuum pump (B) for the exhaust chamber arranged to supply a vacuum to each cylinder when its exhaust valve is open to withdraw exhaust gases out of the cylinder. Vacuum is applied to the exhaust chamber to suck exhaust gases out of the cylinder, the piston is also positively sucked towards the top of the cylinder so that each exhaust stroke is also a power stroke.
To ensure an efficient scavenge, to remove as much of the burnt cases as possible, certain fairly significant overlaps between the opening and closing of inlet and exhaust valves in a top of the cylinder is necessary. Also, the scavenging stroke absorbs a certain amount of mechanical energy to reverse the forces applied to the piston tending at least to unbalance the engine.
It is an object of the invention to overcome or reduce these problems.